This invention relates to vertical float switches and, more particularly, to such switches which incorporate permanent magnets and a moving armature to actuate the switch functions.
Float switches are well known in the art and have been used in such applications as low water fuel cut-off controls which are connected to hot water boilers by way of upper and lower equalizing lines or pipes. The lower equalizing line is coupled to the boiler at a point below the minimum safe water level such that the float within the housing is approximately positioned at the safe water level. The upper equalizing line is connected to the boiler at a point above the minimum safe water level. If during operation of the boiler the water drops below a predetermined critical level, the float in the float chamber drops accordingly and actuates a switch device to activate an external circuit. This control function is then used to turn off a fuel supply such as a burner, to activate an external alarm, to replenish the water deficiency, etc. Float switches of this general type are exemplified in U.S. Pat. No. 3,831,429, which is assigned to the same assignee as the present invention.
Another type of float switch which is known and has been used in the art is the vertical float switch. These float switches utilize the cooperation between a moving armature, which is connected to the float support rod, and a pivotally mounted permanent magnet to actuate a mercury bulb switch. This type of float switch has the advantage that additional switched functions can be added to the switch by vertically cascading a plurality of switch assemblies, each having a separate permanent magnet and associated apparatus. For example, these switches may include the conventional low-water and burner on-off functions, a fuel water pump control, and a third function such as a high-water alarm. Theoretically, any number of desired switches can be added in accordance with the vertical span of the water and the significance of various vertical water levels.
In both of these types of float switches, it has been found that a differential adjustment of the various switch functions is highly desirable. Switch differential is the difference in (water) level between the point where the switch switches on versus the point at which it switches off. For example, once the water level causes the switch to actuate a burner circuit, it is highly desirable that the off function not be attained unless the water drops significantly below the turn on point. Otherwise, the burner can erratically turn on and off in response to a threshold water level situation or turbulence within the hot water boiler. This erractic on-off operation is detrimental of external apparatus such as burners and may pose a nuisance to alarm circuits and the like.
While the vertical float switch does permit a degree of switch differential adjustment, such adjustment is particularly difficult to attain. That is, the adjustment is accomplished by providing a lost-motion in the moving armature of the magnetic assembly. Thus, the vertical motion of the float rod advances the armature toward the permanent magnetic field until the armature captures the magnet and holds same until adjustable stops are reached. Thereafter, the water level must drop a predetermined distance to recover the lost motion whereupon the continued downward movement of the rod moves the armature away from proximity to the permanent magnet. Accordingly, to accomplish adjustment of the switch differential necessitates adjustment of the lost-motion in the armature which, in turn, requires total disassembly of the float switch in order to remove the float rod assembly. This problem is further aggravated by the fact that if a workman must re-adjust his initial adjustment, the float switch must be assembled for a test and then again disassembled to accomplish the final adjustment. In so doing, the hot water boiler may have to be cooled down or at least depressurized in order to accomplish the disassembly as the float chamber of the float switch is essentially an integral communicating part of the hot water boiler. This is a nuisance. Further, any adjustment to the differential effects all switches equally and independent adjustment of the different switches is therefore precluded.
A further disadvantage of these prior art vertical float switches is that inserts are utilized within the float chamber which function as a guide to restrain the vertical translation of the float rod solely along the longitudinal axis of the rod. Since these inserts are therefore in contact with the water, they are subject to contamination and fouling and may result in a jammed or immoveable float rod assembly. This is a problem.
These and other disadvantages are overcome by the present invention wherein there is provided a float switch having means for adjusting the switch differential essentially externally of the float switch housing and without necessitating disassembly of the float switch. The float switch differential may be adjusted with the float switch completely assembled and in communication with a live or operative hot water boiler. That is, the float switch may be externally adjusted while the hot water boiler is in operation and therefore fine adjustments or re-adjustments may be readily accomplished. Further, the adjustment may be performed on each switch independently of the other switches in the cascaded assembly. Still further, the invention also provides means for guiding the float rod assembly within the float switch at a point therein which is substantially removed from the normal water level. Thus, the problems of contamination and the following due to precipitation of the various minerals which are typically found in these hot water boilers are avoided.